This invention relates generally to an external fixation system for bones, and more specifically, to a pin assembly for use in attachment of the external fixation system to the bones and an associated method of use.
In the practice of medicine, and particularly orthopedic medicine, treatment of certain injuries or conditions is accomplished with a system including an external frame that is attached to the bones with pins or wires. Such systems are commonly referred to as orthopedic external fixators or external skeletal fixators. External fixators are commonly utilized to treat acute fractures of the skeleton, soft tissue injuries, delayed union of the skeleton when bones are slow to heal, non-union of the skeleton when bones have not healed, mal-union whereby broken or fractured bones have healed in a mal position, congenital deformities whereby bones develop a mal position, bone infections, bone tumors and bone lengthening, widening or twisting applications. Well known types of external fixators generally include the Ilizarov fixator that is often used for repair of heavily damaged or heavily traumatized bone, the Taylor frame and the limb reconstruction system (LRS).
The use of many external fixators requires multiple pins that are placed through the skin and into the bone. The ends of the pins that stick out from the skin are attached to a rigid framework thereby holding the fractured bone stable so that it can heal.
In many applications, external fixators of this type are preferred over plaster casts because an external fixator can hold the bone fragments much more rigidly than a cast. The advantages of external fixators are that the external frames are quick and easy to apply and provide excellent rigidity and support for specific fractures. If the fracture is open or compound (meaning the skin over the fracture is penetrated) many orthopedic surgeons prefer external fixators because they reliably and securely position the traumatized bone. Examples of external fixators are shown in U.S. Pat. Nos. 5,067,954; 4,978,348; 4,978,347; and 4,615,338 each listing Gavriil Ilizarov as inventor and incorporated herein by reference. Other well known external fixation devices are commercially available from Orthofix Srl of Verona, Italy and Smith & Nephew, Inc. of Memphis, Tenn.
External fixator frames vary considerably in design and capabilities, and may include multiple or single bars, rods or rings and a number of pins or wires connecting the frame to the bony skeleton. The pins or wires may extend completely through the bony skeleton and out each side of the limb or may extend through the bony skeleton and out only one side of the limb. Pins that extend completely through the bony skeleton and out both sides of the limb are commonly referred to as “transfixation pins.” Pins, which extend through the bony skeleton and out only one side of the limb are commonly referred to as “half pins.”
The exact location and orientation of the wires and pins are determined by the physician according to anatomic and mechanical factors. In the course of treatment with external fixation, the precise placement of the external fixator and the associated pins and wires is critical for the proper positioning and healing of the traumatized bone. Even slight movement or repositioning of the pins and associated external fixator frame may result in misalignment and repositioning of the traumatized bone often requiring corrective measures by the treating physician including removal, replacement or readjustment of the pins and/or external fixator in a subsequent surgical or similar procedure.
While external fixators of this type have proven to be very beneficial in many applications, certain disadvantages associated with external fixators are readily acknowledged. Specifically, infection is a primary concern with the use of such devices. The pins protrude through the muscle, subcutaneous tissue and skin. Because biological tissue does not adhere to the metal pins, a chronic break remains in the skin around the pins. Healthy skin, by its nature, is an effective barrier to bacteria entry. During insertion of the pin this barrier is compromised. Scar tissue formed around a pin or wire during healing lacks the blood vessels normally found in healthy tissue. The lack of blood flow at the pin or wire insertion site hinders systemic antibiotic delivery to the site where bacteria can freely enter the body. As a result, a rather common complication involving external fixators is infection occurring around the pins.
Investigations have shown that some superficial infection occurs in approximately fifty percent of the pins used in external fixators. A single external fixator utilizes numerous pins (about 6-12 pins typically) thereby increasing the opportunity for infection. The severities of the infections range from a superficial skin infection to a deep bone infection, i.e., osteomyelitis. Deep bone infections, however, resulting in loosening of the pin-bone interface necessitating return to the operating room occur more rarely.
In addition to the obvious problems associated with the infection that must be addressed, pin tract infection for external fixators commonly leads to pin loosening and, in some cases, requires premature pin removal and replacement with a return to the operating room for sterile pin insertion. The pins securing the external fixator to the bones work loose in the bone that leads to failure of the device. If the external fixator is removed or additional pins are required, the healing process can be significantly compromised. This significantly undermines the effectiveness of the external fixator for proper bone/soft tissue healing.
In addition to infection, pin loosening can result from a number of factors including pin design and placement, bone necrosis due to surgical trauma during pin insertion, abnormal contact pressure at the pin-bone interface from unfavorable axial loading on the pins due to faulty frame design, or delay in fracture healing.
As a result, an external fixator and associated pin attachment system which avoids the above-described problems associated with loosening and provides consistently reliable and secure attachment of the fixation device to the bone is required even in potentially infectious environments.